package top.as.sean.common.id;

import cn.hutool.core.lang.Singleton;

/**
 * 雪花id工具类
 *
 * @author: ArchieSean
 * @create: 2022/11/8
 */
public class SnowflakeId {
    /**
     * 起始的时间戳
     */
    private final static Long START_STAMP = 1667893477133L;

    /**
     * 序列号占用的位数
     */
    private final static Long SEQUENCE_BIT = 12L;
    /**
     *机器标识占用的位数
     */
    private final static Long MACHINE_BIT = 5L;
    /**
     * 数据中心占用的位数
     */
    private final static Long DATACENTER_BIT = 5L;

    /**
     * 每一部分的最大值
     */
    private final static Long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
    private final static Long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private final static Long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static Long MACHINE_LEFT = SEQUENCE_BIT;
    private final static Long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static Long TIMESTAMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;
    /**
     * 数据中心
     */
    private final Long datacenterId;
    /**
     * 机器标识
     */
    private final Long machineId;
    /**
     * 序列号
     */
    private Long sequence = 0L;
    /**
     * 上一次时间戳
     */
    private Long lastStamp = -1L;

    private SnowflakeId(Long datacenterId, Long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    /**
     * 产生下一个ID
     *
     * @return Long
     */
    private synchronized Long nextId() {
        Long curryStamp = getNewsTemp();
        if (curryStamp < lastStamp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (curryStamp.equals(lastStamp)) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                curryStamp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastStamp = curryStamp;

        return
                //时间戳部分
                (curryStamp - START_STAMP) << TIMESTAMP_LEFT
                        //数据中心部分
                        | datacenterId << DATACENTER_LEFT
                        //机器标识部分
                        | machineId << MACHINE_LEFT
                        //序列号部分
                        | sequence;
    }

    private Long getNextMill() {
        long mill = getNewsTemp();
        while (mill <= lastStamp) {
            mill = getNewsTemp();
        }
        return mill;
    }

    private Long getNewsTemp() {
        return System.currentTimeMillis();
    }

    /**
     * 对外提供
     *
     * @return Long
     */
    public static Long createId() {
        return Singleton.get(SnowflakeId.class, 0L, 1L)
                .nextId();
    }
}
